Map setters using map getters

[imaqtkatt]

def main():
  map = { 0: 1, 1: 10 }
  map[map[0]] = 99
  return map[map[0]]

Expected: 99
Actual:

thread 'main' panicked at /home/martin/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bend-lang-0.2.18/src/imp/to_fun.rs:366:30:
internal error: entered unreachable code
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic
   3: bend::imp::to_fun::<impl bend::imp::Expr>::to_fun
   4: bend::imp::to_fun::<impl bend::imp::Stmt>::into_fun
   5: bend::imp::to_fun::<impl bend::imp::Stmt>::into_fun
   6: bend::fun::parser::TermParser::parse_book
   7: bend::execute_cli_mode::{{closure}}
   8: bend::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.